The present invention generally relates to analog clocks, and more particularly to an analog clock in which hands (pointers) thereof are rotationally driven by a stepping motor.
A conventional analog clock is provided with an adjusting shaft, and the time is adjusted by rotating this adjusting shaft. But when this analog clock is used as a built-in clock of an automobile, there is a problem from the point of view of the design in that the adjusting shaft must project from a clockface through a hole in a front glass of the clock. On the other hand, when the analog clock is arranged within an instrument panel together with a speedometer and the like, it is necessary to provide a hole in a glass which covers the instrument panel so that the adjusting shaft can project from the clockface through this hole.
For this reason, there conventionally are analog clocks which can be adjusted by remote control. Such remote controlled analog clocks may be divided into first and second types. The analog clock of the first type employs two motors, that is, a clock motor for driving the clock and an adjusting motor for driving the adjusting shaft. The analog clock of the second type employs a single stepping motor for driving the clock, and when adjusting the time, this stepping motor is rotated in a forward or reverse direction at a speed which is high compared to that when the stepping motor is rotated to keep the time.
The analog clock of the first type requires the adjusting motor for driving the adjusting shaft, gears for transmitting the rotation of the adjusting motor to the adjusting shaft, a clutch mechanism for meshing a gear of the adjusting shaft with a gear of a minute hand shaft and the like. Hence, there is a problem in that the analog clock of the first type is complex and expensive.
On the other hand, the analog clock of the second type supplies to a coil a pulse signal for forward rotation having a narrow pulse width so as to slightly urge a rotor in the forward direction, and rotates the rotor in the reverse direction by supplying to the coil a pulse signal for reverse rotation having a sufficiently wide pulse width with a timing with which the rotor reacts to the urging force and moves in the reverse direction. For this reason, when the size or the like of the stepping motor is changed, it is necessary to produce a pulse signal for reverse rotation having a timing peculiar to that stepping motor when rotating the rotor in the reverse direction. Thus, the size or the like of the analog clock cannot be changed arbitrarily without changing the timing of the pulse signal for reverse rotation, and the design of the analog clock cannot be changed with ease. Furthermore, there is a problem in that the analog clock of the second type may perform an erroneous operation such as missing a step movement and performing a step movement in a wrong direction when subjected to external vibration, shock and the like.